Electric brush unit



Feb. 24, 1970 A. J. SHALER 3,497,741

ELECTRIC BRUSH UNI T Filed June 25, 1968 '2 Sheets-Sheet 1 INVENTOR AMOS J. SHALL-w W l BY ATTORNEYS.

Feb. 24, 1970 A. J. SHALER ELECTRIC BRUSH UNIT Filed June 25, 1968 2 Sheets-Sheet 2 INVENTOR 44105 J. 55mm ATTORNEYS.

United States Patent 3,497,741 ELECTRIC BRUSH UNIT Amos J. Shaler, State College, Pa., assignor to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Filed June 25, 1968, Ser. No. 739,854 Int. Cl. H02k /14 US. Cl. 310-246 8 Claims ABSTRACT OF THE DISCLOSURE A brush holder device for long brushes wherein the brush tension is maintained, throughout the life of the brush, betwen allowable limits of pressure applied by a single brush spring which is recompressed at several essentially equal intervals of the total brush wear by a stiff spring in series relation with said first spring. This is accomplished by a series of detent's sequentially allowing expansion of the stiff spring thereby retensioning said single spring to its original value in a series of steps controlled by the amount of wear of said brush.

A majority of the millions of electric motors used annually in electrical appliances for home and industry are considered to have failed beyond repair and are scrapped when any one of the vital motor components fails. This often results in discarding the entire appliance. Past causes of motor failures, such as loss of electrical insulation and excessive bearing wear, have been overcome to a large extent, so that nowadays the principal cause of failure is the wearing out of the brushes. Accordingly, the search for ways of extending the useful brush life of generators and motors is a continuing one and is becoming increasingly important. An obvious way to increase brush life is to start with a longer brush, but for several practical reasons the length of the brush holder usually cannot be increased to accommodate a longer brush. Any attempt to use a longer brush by shortening the coil spring that presses it against the rotating current collector has been a failure because the pressure of the brush against the collector must only vary between narrow limits. A shorter spring will not press the brush firmly enough against the collector when the brush nears the end of its life, or, if a short but stronger spring is used, it will press the brush so tightly against the collector in the beginning that excessive wear will occur.

It is among the objects of this invention to provide an electric brush unit, in which a holder of a given length can accommodate a longer brush than heretofore, and yet the pressure of the brush against a rotating current collector always remains between the maximum and minimum desired for eflicient contact and minimum wear.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a longitudinal section through a brush unit, showing the brush when it is new;

FIG. 2 is a similar view, but shows the brush partially worn away;

BIG. 3 likewise is a similar view, but shows the brush after it has worn away the maximum amount permitted; and

FIGS. 4 and 5 are enlarged cross sections taken on the lines IVIV and V-V, respectively, of FIG. 1.

Referring to FIGS. 1, 4 and 5 of the drawings, a brush holder cartridge is formed from a tubular member 1, one end of which is closed at least to some extent. For example, it may be closed by a cap 2 that may be screwed onto the tube. This cartridge is adapted to be supported in any suitable manner beside a rotating current collector "ice 3, such as a commutator or slip ring. The cartridge extends radially away from the collector, with its open front end adjacent the collector. Inside the cartridge there is a pair of elongated or strip-like resilient racks 4 extending length-wise of it. These racks face each other at opposite sides of the carridge. The front ends of the racks are secured to the open end portion of the cartridge by rivets 5 or the like. The racks are shaped to normally converge toward the closed end of the cartridge so that their rear ends will be close togeher or actually touch and press against each other, as shown in FIG. 3, when there is no 'brush holding them apart. These rear ends are spaced a short distance from cap 2 that closes the adjacent rear end of the cartridge.

When the holder is in use, a current conducting brush, such as a carbon brush 7, is disposed between the two racks. The brush is rectangular in cross section and when it is new its rear end is between the rear ends of the racks, which it springs apart, and its front end projects from the open end of the cartridge a short distance to engage the current collector 3. The brush is considerably longer than a brush could be for the same holder containing a conventional spring. To center the brush in the cartridge and guide it as its exposed front end is worn away, the opposite edges of each rack are provided with inwardly projecting flanges 8 that receive the brush between them. Each flange is provided with a plurality of longitudinally spaced notches 9 so that the racks can bend or flex at predetermined points along their length. When a new brush is pushed into the cartridge betwen the racks, it spreads their rear ends apart and the racks become more or less parallel to the adjacent side wall of the cartridge as seen in FIG. 1. The rear end of the brush may be provided with a pig tail 10 that extends out through a central opening in the end cap. Or, if desired, an electric lead can be secured to the cartridge directly. The rear end of the brush may be covered by a metal clip 11, which can be considered part of the brush.

Slidingly disposed in cartridge 1 in the relatively short space between its cap and the rear end of the brush is a spring housing that has spaced concentric inner and outer cylindrical side walls 12 and 13, which are connected at their front ends by a transverse end wall 14. The housing is pressed against the brush or the adjoining ends of the racks by an outer coil spring 15 compressed between the cartridge cap and housing end wall 14. Inside the central area of the housing there is an inner coil spring 16 that is compressed between the rear end of the brush and a transverse wall or flange 17 at the rear end of the housing. This spring, which is weaker than the other spring, presses the brush against the current collector.

The outer side of each of the racks 4 is provided with longitudinally spaced laterally projecting teeth 20, and spring housing wall 14 has a pair of openings 21 therein larger than the teeth and the adjoining ends of the racks, but offset toward each other from the rearmost pair of teeth far enough for those teeth to engage the adjoining end of the spring housing beside those openings, as shown in FIG. 1. Consequently, the spring housing is held close to the cartridge cap even if the brush does not touch the housing, and the outer coil spring 15 is held compressed.

As the front end of the brush wears away against the current collector 3, the inner coil spring 16 expands as indicated in dotted lines in FIG. 1 and slowly pushes the brush forward out of the cartridge. As the rear end of the brush moves toward the front end of the cartridge, the resilient racks are allowed to move toward each other across the end of the brush until the rearmost pair of rack teeth have moved toward each other far enough to enable the outer coil spring to push the spring housing forward past them and along the racks toward the next pair of teeth, which are farther apart than the rearmost pair and therefore stop further movement of the housing, as shown in FIG. 2. The ends of openings 21 are provided with lateral extensions that accommodate rack flanges 8. A given tooth on a given rack does not release the spring housing until the rear end of the brush has moved far enough to reach the first pair of gaps 9 in the rack flanges. At that point the resilient rack can bend itself toward the other rack so that the adjoining housing opening 21 can receive and move forward over the first tooth 20. This occurs before the inner spring has expanded so far that the brush would be held against the collector ring with insuflicient pressure. On the other hand, the pressure exerted by either spring when fully compressed is such that the brush will never be held against the collector too tightly, which would cause unnecessary Wear. Expansion of the stronger outer coil spring when the spring housing slips over a pair of rack teeth causes the housing to compress the inner spring again as shown in FIG. 2.

As the brush continues to wear, the operation just described is repeated periodically; that is, the inner spring pushes the brush forward until the spring housing can 7 slip over the next pair of teeth and move along the rack and thereby recompress the inner spring. After the spring housing has been moved as far as possible by the outer coil spring, which recompresses the inner coil spring for the last time, the inner spring is still free to expand and continue to press the brush against the collector until there is only a very short brush stub left in the cartridge, as shown in FIG. 3.

-By using the two concentric coil springs, the outer one of which periodically recompresses the inner one, springs can be used which are shorter in their fully compressed state than the single spring in a conventional brush holder. The important result of this is that less space is required in the holder for the shorter springs, so the brush can be made longer to occupy the space thus saved. Consequently, if the brush in a given unit can be made 10 percent longer than heretofore, for example, then the life of the motor or generator with which the brush is used should be extended by a like amount, and that may be a considerable period of time.

If desired, the outer side wall of the spring housing can be omitted, but it is believed that the housing will move more smoothly if that wall is present.

According to the provisions of the patent statutes, I have explained the princi le of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. An electric brush unit comprising a tubular cartridge adapted to be mounted radially of a rotating current collector and having a closed rear end and an open front end, a pair of strip-like resilient racks extending lengthwise of the inside of the cartridge and normally converging rearwardly therein with their front ends spaced apart and secured to the opposite sides of the cartridge at said open end and with their rear ends spaced from said closed end, the outer side of each of said racks being provided with longitudinally spaced laterally projecting teeth, a current conducting brush disposed in the cartridge between said racks and having a front end projecting from said open end, the rear end of the brush being spaced from the closed end of the cartridge and springing the rear ends of the racks apart, a spring housing slidingly disposed in the cartridge between its closed end and the rear end of the brush and provided at its front end with a pair of openings larger than said teeth but offset toward each other from the rearmost pair of teeth far enough for those teeth to engage the front end of the housing beside the openings, an inner coil spring in the housing between said openings, the spring being compressed between the rear end of the brush. and the housing and urging the brush forward toward the open end of the cartridge, and an outer coil spring in the cartridge stronger than the inner spring and compressed between said closed end and said housing around said openings, whereby as the front end of the brush wears away the inner coil spring will expand and push the brush forward out of the cartridge until said rearmost pair of rack teeth can move toward each other far enough to permit the outer coil spring to push the housing forward past them and along the racks into engagement with the next pair of teeth and thereby recompress the inner coil spring.

2. An electric brush unit according to claim 1, in which said spring housing. has a cylindrical central portion extending from said brush toward said closed end of the cartridge, and laterally projecting portions at its front end provided withsaid openings, said inner coil spring being housed in said cylindrical portion.

3. An electric. brush unit according to claim 1, in which said spring housing has a pair of spaced concentric 'cylindrical portions extending from its front end toward said closed end of the cartridge, and laterally extending connecting portions integrally connecting the front ends of said cylindrical portions and provided with said openings, said inner coil spring being housed in the inner cylindrical potrion and said outer coil spring being housed in the outer cylindrical portion.

4. An electric brush unit according to claim 1, in which each of said racks is provided with inwardly projecting side flanges guiding said brush, the flanges having longitudinally spaced notches therein between said teeth to permit flexing of the racks at longitudinally spaced points.

5. An electric brush unit according. to claim 4, in which said flexing points adjoin the sides of said teeth facing the closed end of the cartridge.

6. An electric brush unit according to claim 1, in which said outer coil spring is capable of expanding far enough to push said housing as far forward along said racks as the housing can move.

7. An electric brush unit according to claim 1, in which the pressures exerted by said inner coil spring upon the brush always remain between the maximum and minimum minimum pressure.

References Qited UNITED STATES PATENTS 462,973 11/1891 Thomson et a1 -310-426 2,813,208 11/1957 Ritter 310 -247 2,862,124

11/1958 Huber 310-246 J. D. MILLER, Primary Examiner L. L. SMITH, Assistant Examiner 1 

